Method for controlling of valve timing of continuous variable valve duration engine

ABSTRACT

A method for controlling valve timing is provided for an engine including continuous variable duration (CVVD) device disposed on both intake valve and exhaust valve sides respectively. The method may include: classifying control regions into first, second, third, fourth, and fifth control regions based on engine load and speed; applying a maximum duration to an intake valve and controlling a valve overlap in a first control region, applying the maximum duration to the intake valve and exhaust valve in the second control region; controlling a manifold absolute pressure (MAP) of an intake manifold to be maintained consistently in the third control region; controlling a throttle valve to be fully opened, advancing an intake valve closing (IVC) timing, and controlling an exhaust valve closing (EVC) timing to after top dead center in the fourth control region; and controlling a wide open throttle valve (WOT) and retarding the intake valve closing in the fifth control region.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2015-0176333, filed on Dec. 10, 2015, the entirecontents of which are incorporated herein by reference.

FIELD

The present disclosure relates to a system and a method for controllingvalve timing of a continuous variable valve duration engine.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

An internal combustion engine combusts mixed gas in which fuel and airare mixed at a predetermined ratio through a set ignition mode togenerate power by using explosion pressure.

Generally, a camshaft is driven by a timing belt connected with acrankshaft that converts linear motion of a cylinder by the explosionpressure into rotating motion to actuate an intake valve and an exhaustvalve, and while the intake valve is opened, air is suctioned into acombustion chamber, and while an exhaust valve is opened, gas which iscombusted in the combustion chamber is exhausted.

To improve the operations of the intake valve and the exhaust valve andthereby improve engine performance, a valve lift and a valveopening/closing time (timing) may be controlled according to arotational speed or load of an engine. Therefore, a continuous variablevalve duration (CVVD) device controlling the opening duration of anintake valve and an exhaust valve of the engine and a continuousvariable valve timing (CVVT) device controlling the opening and closingtiming of the intake valve and the exhaust valve of the engine have beendeveloped.

The CVVD device may control opening duration of the valve. In addition,the CVVT device may advance or retard the opening or closing timing ofthe valve in a state where the opening duration of the valve is fixed.That is, if the opening timing of the valve is determined, the closingtiming is automatically determined according to the opening duration ofthe valve.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the present disclosureand therefore it may contain information that does not form the priorart that is already known to a person of ordinary skill in the art.

SUMMARY

The present disclosure provides a system and a method for controllingvalve timing of a continuous variable valve duration engine thatcontrols duration of the valve being equipped with a continuous variableduration device disposed on an intake valve side and exhaust valve side.

A method for controlling valve timing provided with a continuousvariable duration (CVVD) device disposed on both intake valve side andexhaust valve sides respectively may include classifying a plurality ofcontrol regions depending on an engine speed and an engine load. The aplurality of control regions may include: a first control region whenthe engine load is less than a first predetermined load; a secondcontrol region when the engine load is greater than or equal to thefirst predetermined load and less than a second predetermined load; athird control region when the engine load is greater than or equal tothe second predetermined load and less than a third predetermined load;a fourth control region when the engine load is greater than or equal tothe second predetermined load and the engine speed is less than apredetermined speed; and a fifth control region when the engine load isgreater than or equal to the third predetermined load and the enginespeed is greater than or equal to the predetermined speed

The method for controlling valve timing further includes; applying amaximum duration to an intake valve and controlling a valve overlap byusing the exhaust valve in the first control region; applying themaximum duration to the intake valve and exhaust valve in the secondcontrol region; controlling a manifold absolute pressure (MAP) of anintake manifold to be maintained consistently in the third controlregion; controlling a throttle valve to be fully opened, advancing anintake valve closing (IVC) timing, and controlling an exhaust valveclosing (EVC) timing to after a top dead center in the fourth controlregion; and controlling a wide open throttle valve (WOT) and retardingthe intake valve closing.

If the control region is in the first control region, then thecontroller may control the intake valve closing (IVC) timing to be fixedand control the exhaust valve closing (EVC) timing to be set up at amaximum value within sustainable combust stability in order to limit avalve overlap.

If the control region is in the second control region, then thecontroller may control the exhaust valve closing (EVC) timing to be lateas the engine load is increased in order that the exhaust valve reachesthe maximum duration.

If the control region is in the third control region, then thecontroller may advance both the exhaust valve closing (EVC) timing andthe intake valve closing (IVC) timing in order to maintain the MAPconsistently even if the engine load is increased.

If the control region is in the fourth region, then the controller mayretard the intake valve closing (IVC) timing and controls the exhaustvalve closing (EVC) timing to approach a top dead center in order toinhibit or prevent from generating the valve overlap.

A system for controlling valve timing of a continuous variable valveduration engine may include: a data detector detecting data related to arunning state of a vehicle; a camshaft position sensor detecting aposition of a camshaft; an intake continuous variable valve duration(CVVD) device controlling an opening time of an intake valve of theengine; an exhaust continuous variable valve duration (CVVD) devicecontrolling an opening time of an exhaust valve of the engine; acontroller configured to classify the running state of the vehicle intoa plurality of control regions depending on an engine speed and anengine load based on signals from the data detector and camshaftposition sensor, and configured to control the intake CVVD device andthe exhaust CVVD device according to the control regions.

The a plurality of control regions may include: a first control regionwhen the engine load is less than a first predetermined load; a secondcontrol region when the engine load is greater than or equal to thefirst predetermined load and less than a second predetermined load; athird control region when the engine load is greater than or equal tothe second predetermined load and less than a third predetermined load;a fourth control region when the engine load is greater than or equal tothe second predetermined load and the engine speed is less than apredetermined speed; and a fifth control region when the engine load isgreater than or equal to the third predetermined load and the enginespeed is greater than or equal to the predetermined speed.

The controller may apply a maximum duration to the intake valve andlimit a valve overlap by using the exhaust valve in the first controlregion, apply the maximum duration to the intake and exhaust valves inthe second control region, control a manifold absolute pressure (MAP) inan intake manifold to be maintained consistently in the third controlregion, control a wide open throttle valve (WOT) and advance an intakevalve closing (IVC) timing and control an exhaust valve closing (EVC)timing to after a top dead center (TDC) in the fourth control region,and control a wide open throttle valve (WOT) and retards the IVC timingin the fifth control region.

The controller may control the intake valve closing (IVC) timing to befixed and control the exhaust valve closing (EVC) timing to be set up ata maximum value within sustainable combust stability in order to limit avalve overlap in the first control region.

The controller may control the exhaust valve closing (EVC) timing to belate as the engine load is increased in order that the exhaust valvereaches the maximum duration in the second control region.

The controller may advance both an exhaust valve closing (EVC) timingand the intake valve closing (IVC) timing in order to maintain the MAPconsistently when the engine load is increased in the third controlregion.

The controller may retard the intake valve closing (IVC) timing andcontrols the exhaust valve closing (EVC) timing to approach a top deadcenter in order to inhibit or prevent from generating the valve overlapin the fifth control region.

As described above, according to an exemplary form of the presentdisclosure, duration and timing of the continuous variable valve aresimultaneously controlled, so the engine may be controlled underdesirable conditions.

That is, since opening timing and closing timing of the intake valve andthe exhaust valve are appropriately controlled, the fuel efficiencyunder a partial load condition and engine performance under a high loadcondition are improved. In addition, a starting fuel amount may bereduced by increasing a valid compression ratio, and exhaust gas may bereduced by shortening time for heating a catalyst.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a schematic block diagram showing a system for controllingvalve timing of a continuous variable valve duration engine according toone form of the present disclosure;

FIG. 2 is a perspective view showing a continuous variable valveduration device which is disposed on intake valve and exhaust valvesides according to one form of the present disclosure;

FIG. 3A and FIG. 3B are flowcharts showing a method for controllingvalve timing of a continuous variable valve duration engine according toone form of the present disclosure;

FIGS. 4A-4C are graphs showing duration, opening timing, and closingtiming of an intake valve depending on an engine load and an enginespeed according to the present disclosure; and

FIGS. 5A-5C are graphs showing duration, opening timing, and closingtiming of an exhaust valve depending on an engine load and an enginespeed according to the present disclosure.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

As those skilled in the art would realize, the described forms may bemodified in various different ways, all without departing from thespirit or scope of the present disclosure.

Throughout this specification and the claims which follow, unlessexplicitly described to the contrary, the word “comprise” and variationssuch as “comprises” or “comprising” will be understood to imply theinclusion of stated elements but not the exclusion of any otherelements.

It is understood that the term “vehicle” or “vehicular” or other similarterms as used herein is inclusive of motor vehicles in general includinghybrid vehicles, plug-in hybrid electric vehicles, and other alternativefuel vehicles (e.g., fuels derived from resources other than petroleum).As referred to herein, a hybrid electric vehicle is a vehicle that hastwo or more sources of power, for example a gasoline-powered andelectric-powered vehicle.

Additionally, it is understood that some of the methods may be executedby at least one controller. The term controller refers to a hardwaredevice that includes a memory and a processor configured to execute oneor more steps that should be interpreted as its algorithmic structure.The memory is configured to store algorithmic steps, and the processoris specifically configured to execute said algorithmic steps to performone or more processes which are described further below.

Furthermore, the control logic of the present disclosure may be embodiedas non-transitory computer readable media on a computer readable mediumcontaining executable program instructions executed by a processor, acontroller, or the like. Examples of computer readable media include,but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetictapes, floppy disks, flash drives, smart cards, and optical data storagedevices. The computer readable recording medium can also be distributedin network coupled computer systems so that the computer readable mediais stored and executed in a distributed fashion, e.g., by a telematicsserver or a controller area network (CAN).

FIG. 1 is a schematic block diagram showing a system for controllingvalve timing of a continuous variable valve duration engine according toone form of the present disclosure;

As shown in FIG. 1, a system for controlling valve timing of acontinuous variable valve duration engine includes: a data detector 10,a camshaft position sensor 20, a controller 30, an intake continuousvariable valve duration (CVVD) device 40, and an exhaust continuousvariable valve duration (CVVD) device 50.

The data detector 10 detects data related to a running state of thevehicle for controlling the CVVD devices, and includes a vehicle speedsensor 11, an engine speed sensor 12, an oil temperature sensor 13, anair flow sensor 14, and an accelerator pedal position (APS) sensor 15,although other sensors may be employed.

The vehicle speed sensor 11 detects a vehicle speed, transmits acorresponding signal to the controller 30, and may be mounted at a wheelof the vehicle.

The engine speed sensor 12 detects a rotation speed of the engine from achange in phase of a crankshaft or camshaft, and transmits acorresponding signal to the controller 30.

The oil temperature sensor (OTS) 13 detects temperature of oil flowingthrough an oil control valve (OCV), and transmits a corresponding signalto the controller 30.

The oil temperature detected by the oil temperature sensor 13 may bedetermined by measuring a coolant temperature using a coolanttemperature sensor mounted at a coolant passage of an intake manifold.Therefore, in one form, the oil temperature sensor 13 may include acoolant temperature sensor, and the oil temperature should be understoodto include the coolant temperature.

The air flow sensor 14 detects an air amount drawn into the intakemanifold, and transmits a corresponding signal to the controller 30.

The accelerator pedal position sensor (APS) 15 detects a degree in whicha driver pushes an accelerator pedal, and transmits a correspondingsignal to the controller 30. The position value of the accelerator pedalmay be 100% when the accelerator pedal is pressed fully, and theposition value of the accelerator pedal may be 0% when the acceleratorpedal is not pressed at all.

A throttle valve position sensor (TPS) that is mounted on an intakepassage may be used instead of the accelerator pedal position sensor 15.Therefore, in one form, the accelerator pedal position sensor 15 mayinclude a throttle valve position sensor, and the position value of theaccelerator pedal should be understood to include an opening value ofthe throttle valve.

The camshaft position sensor 20 detects a change of a camshaft angle,and transmits a corresponding signal to the controller 30.

FIG. 2 is a perspective view showing a continuous variable valveduration device which is disposed on intake valve and exhaust valvesides according to one form of the present disclosure.

As shown in FIG. 2, the continuous variable valve duration device 40, 50are mounted at the intake and exhaust valve sides respectively throughopening and fixed type apparatus. And an intake valve opening (IVO)timing and an exhaust valve opening (EVO) timing are fixed. For example,the IVO timing may be fixed at an angle of approximately 0 to 10 degreesafter a top dead center (TDC), since it is advantageous for fuelefficiency when the IVO timing is close to the top dead center in mostcontrol regions. Otherwise, the EVO timing may be fixed at an angle ofapproximately 40 to 50 before a bottom dead center (BDC) due to havingadvantageous for fuel efficiency in most control regions.

The intake continuous variable valve duration (CVVD) device 40 controlsan opening time of an intake valve of the engine according to a signalfrom the controller 30, the exhaust continuous variable valve duration(CVVD) device 50 controls an opening time of an exhaust valve of theengine according to a signal from the controller 30.

The controller 30 may classify a plurality of control regions dependingon an engine speed and an engine load based on signals from the datadetector 10 and camshaft position sensor 20, and the controller 30controls the intake CVVD device 40 and the exhaust CVVD device 50according to the control regions. Herein, the plurality of controlregions may be classified into five regions.

The controller 30 applies a maximum duration to the intake valve andlimits a valve overlap by using the exhaust valve in a first controlregion. The controller 30 applies the maximum duration to the intake andexhaust valves in a second control region, controls a manifold absolutepressure (MAP) in an intake manifold to be maintained consistently in athird control region. And the controller 30 controls a wide openthrottle valve (WOT), advances an intake valve closing (IVC) timing, andcontrols an exhaust valve closing (EVC) timing to after the top deadcenter (TDC) in a fourth control region. Further, the controller 30controls a wide open throttle valve (WOT) and retards the IVC timing inthe fifth control region.

For these purposes, the controller 30 may be implemented as at least oneprocessor that is operated by a predetermined program, and thepredetermined program may be programmed in order to perform each step ofa method for controlling valve timing of a continuous variable valveduration engine.

Various forms described herein may be implemented within a recordingmedium that may be read by a computer or a similar device by usingsoftware, hardware, or a combination thereof.

For example, the hardware of the forms described herein may beimplemented by using at least one of application specific integratedcircuits (ASICs), digital signal processors (DSPs), digital signalprocessing devices (DSPDs), programmable logic devices (PLDs), fieldprogrammable gate arrays (FPGAs), processors, controllers,micro-controllers, microprocessors, and electrical units designed toperform any other functions.

The software such as procedures and functions of the forms described inthe present disclosure may be implemented by separate software modules.Each of the software modules may perform one or more functions andoperations described in the present disclosure. A software code may beimplemented by a software application written in an appropriate programlanguage.

Hereinafter, a method for controlling valve timing of a continuousvariable valve duration engine according to one form of the presentdisclosure will be described in detail with reference to FIG. 3A to FIG.5C.

FIG. 3A and FIG. 3B are flowcharts showing a method for controllingvalve timing of a continuous variable valve duration engine.

FIGS. 4A-4C are graphs showing duration, opening timing, and closingtiming of an intake valve depending on an engine load and an enginespeed; and FIGS. 5A-5C are graphs showing duration, opening timing, andclosing timing of an exhaust valve depending on an engine load and anengine speed.

As shown in FIG. 3A and FIG. 3B, a method for controlling valve timingof a continuous variable valve duration engine starts with classifying aplurality of control regions depending on an engine speed and an engineload by the controller 30 at step S100.

The control regions will be described with reference to FIG. 4A to FIG.5C. The first to fifth control regions are indicated in the FIG. 4A toFIG. 5C.

The controller 30 may classify control regions as a first control regionwhen the engine load is less than a first predetermined load, a secondcontrol region when the engine load is greater than or equal to thefirst predetermined load and less than a second predetermined load, anda third control region when the engine load is greater than or equal tothe second predetermined load and less than a third predetermined load.In addition, the controller 30 may classify control regions as a fourthregion when the engine load is greater than or equal to the secondpredetermined load and the engine speed is less than a predeterminedspeed, a fifth region when the engine load is greater than or equal tothe third predetermined load and the engine speed is greater than orequal to the predetermined speed.

Meanwhile, referring to FIG. 4A to FIG. 5C, a crank angle is marked inan intake valve duration (IVD) map and an exhaust valve duration (EVD)map, which indicating the opening time of the intake valve and exhaustvalve. For example, regarding the IVD map in the FIG. 4A, a curved linewritten as a number 220 at inner side of the fifth region means that thecrank angle is approximately 220 degree. Although not shown in thedrawing, the crank angle which is more than approximately 220 degree andless than approximately 240 degree is positioned between the curved lineof the number 220 and the curved line of the number 240.

In addition, a unit of number designated in an intake valve opening(IVO) timing map is before a top dead center (TDC), a unit of numberdesignated in an intake valve closing (IVC) timing map is after a bottomdead center (BDC), a unit of number designated in an exhaust valveopening (EVO) timing map is before BDC, and a unit of number designatedin an exhaust valve closing (EVC) map is after TDC.

Each region and curved line in the FIG. 4A to FIG. 5C are an example ofone form of the present disclosure, it may be modified within thetechnical idea and scope of the present disclosure.

After classifying the control regions based on the engine speed and loadin the step of S100, the controller 30 determines whether the presentengine state is under the first control region at step S110.

In the step of S110, if the engine load is less than a firstpredetermined load, the controller 30 determines that the engine stateis under the first control region. At this time, the controller 30applies a maximum duration to the intake valve and controls the valveoverlap between the exhaust valve and intake valve at step S120. Thevalve overlap is in a state where the intake valve is opened and theexhaust valve is not closed yet.

In other words, in the first control region in which the engine state isunder low load, since the IVO timing is fixed, the controller 30 maycontrol the IVC timing at a LIVC position (Late Intake Valve Closing;e.g. approximately 100-110 degrees after the BDC) by applying a maximumduration to intake valve. At this time, as shown in FIG. 4C, the IVCtiming may be controlled at an angle of approximately 100-110 degreesafter the BDC.

In addition, the controller 30 may move the EVC timing in a direction ofafter TDC to be set up at a maximum value within sustainable combuststability. Meanwhile, as the valve overlap is increased, the fuelconsumption is cut, whereas the combust stability is deteriorated.Accordingly, properly setting the valve overlap is desired. However,according to the form of the present disclosure, it is possible to gethighly improved fuel-efficiency by setting a valve overlap up, whichfixing the EVO timing and controlling the EVC timing to be set up atmaximum value within sustainable combust stability. The timing value maybe determined by predetermined map. Since EVC timing is retarded, theexhaust duration may be increased.

When the current engine state does not belong to the first controlregion at the step S110, the controller 30 determines whether thecurrent engine state belongs to the second control region at step S130.

In the step of S130, if the engine load is more than or equal to thefirst predetermined load and less than the second predetermined load,the controller 30 determines that the engine state is under the secondcontrol region. At this time, the controller 30 controls both the intakevalve and exhaust valve respectively having the maximum durationconsistently at step S140.

The controller 30 may control the EVC timing to be late as the engineload is increased in order that the exhaust valve reaches the maximumduration. Herein, the controller 30 fixes the IVC timing for applyingthe maximum duration to the intake valve in the first control region,thereby the controller 30 may apply maximum duration to the exhaustvalve such that the difference between the atmospheric pressure and thepressure of the intake manifold is maintained at a predetermined value.For example, manifold absolute pressure (MAP), which is the differencebetween atmospheric pressure and pressure of intake manifold, may beapproximately 950 hPa.

When the current engine state does not belong to the second controlregion at the step S130, the controller 30 determines whether thecurrent engine state belongs to the third control region at step S150.

In the step of S150, if the engine load is more than or equal to thesecond predetermined load and less than the third predetermined load,the controller 30 determines that the engine state is under the thirdcontrol region. At this time, the controller 30 controls the MAP to bemaintained consistently at step S160.

In other words, the controller 30 applies the maximum duration to theintake valve and the exhaust valve and controls the MAP to be maintainedconsistently in the second control region. And after, when the enginestate is under the third control region as the engine load is increased,the controller 30 may advance both the EVC timing and IVC timing andcontrols the MAP to be maintained consistently.

Referring to the FIGS. 4A to 5C, the IVC timing and the EVC timing areadvanced in the third region so as to maintain the MAP. The IVO timingmay be fixed, thereby the valve overlap may be shorten and the knockingmay be decreased.

When the current engine state does not belong to the third controlregion at the step S150, the controller 30 determines whether thecurrent engine state belongs to the fourth control region at step S170.

If the engine load is greater than or equal to the second predeterminedload and the engine speed is less than predetermined speed in the S170,the controller 30 determines that the engine state is under the fourthcontrol region. At this time, the controller 30 fully opens a throttlevalve (WOT; Wide Open Throttle valve), advances the IVC timing, andcontrols the EVC timing to after the top dead center (TDC) at step S180.

In the fourth control region in which the engine speed is lower than apredetermined speed (e.g., approximately 1500 rpm), the controller 30should control the EVO timing close to the bottom dead center (BDC) toavoid an exhaust interference. However, the EVO timing may be fixed.Therefore, even if the controller 30 controls the EVC timing to after atop dead center (TDC), generation of the exhaust interference isinevitable.

Moreover, since the IVO timing is fixed, generating scavenging isdifficult although the IVC timing is controlled to be advanced.Therefore, in the fourth control region, the engine performance may bedeteriorated. Accordingly, the form of the present disclosure may besuitable for a hybrid vehicle having sub-power source.

When the current engine state does not belong to the fourth controlregion at the step S170, the controller 30 determines whether thecurrent engine state belongs to the fifth control region at step S190.

In the S190, if the engine load is greater than or equal to the thirdpredetermined load and the engine speed is greater than or equal to thepredetermined speed, then the controller 30 determines that the enginestate is under the fifth control region. At this time, the controller 30fully opens a throttle valve (WOT; Wide Open Throttle valve) and retardsthe IVC timing S200.

If the engine speed greater than or equal to the predetermined speed(e.g., approximately 1500 rpm) in the fifth control region, thecontroller 30 may control the IVC timing to be late according to theengine speed. Referring to the FIGS. 4A-4C, the IVC timing may begradually retarded from at an angle of approximately 20 degrees when theengine speed is less then predetermined speed (low speed) to at angle ofapproximately 60 degrees as the engine speed is increased.

However, the IVO timing may be fixed, thereby, generating the valveunderlap by the IVO timing is unavailable. Therefore, the engineperformance may be restricted in the medium speed (e.g., approximately1500-3000 rpm).

Meanwhile, the controller 30 may retard the IVC timing and may controlthe EVC timing to approach the top dead center in order to inhibit orprevent from generating the valve overlap. The scavenging generated byincreasing back pressure is disappeared in the fifth control region. Andthe EVO timing may be fixed at angle of approximately 40-50 degreesbefore the bottom dead center favorable to pumping exhaust. Accordingly,the valve overlap is decreased as the EVC timing is controlled close tothe top dead center.

As described above, duration and timing of the continuous variable valveare simultaneously controlled, so the engine may be controlled underdesirable conditions.

That is, since opening timing and closing timing of the intake valve andthe exhaust valve are appropriately controlled, the fuel efficiencyunder a partial load condition and engine performance under a high loadcondition are improved. In addition, a starting fuel amount may bereduced by increasing a valid compression ratio, and exhaust gas may bereduced by shortening time for heating a catalyst.

While this present disclosure has been described in connection with whatis presently considered to be practical forms, it is to be understoodthat the present disclosure is not limited to the disclosed forms. Onthe contrary, it is intended to cover various modifications andequivalent arrangements included within the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for controlling valve timing providedwith a continuous variable duration (CVVD) device disposed on bothintake valve side and exhaust valve sides respectively, the methodcomprising: classifying, by a controller, a plurality of control regionsdepending on an engine speed and an engine load, wherein the pluralityof control regions comprises: a first control region determined by thecontroller when the engine load is less than a first predetermined load,a second control region determined by the controller when the engineload is greater than or equal to the first predetermined load and lessthan a second predetermined load, a third control region determined bythe controller when the engine load is greater than or equal to thesecond predetermined load and less than a third predetermined load, afourth control region determined by the controller when the engine loadis greater than or equal to the second predetermined load and the enginespeed is less than a predetermined speed, and a fifth control regionwhen the engine load is greater than or equal to the third predeterminedload and the engine speed is greater than or equal to the predeterminedspeed; applying, by the controller, a maximum duration to an intakevalve and controlling a valve overlap by using an exhaust valve in thefirst control region, applying, by the controller, the maximum durationto the intake valve and exhaust valve in the second control region;controlling, by the controller, a manifold absolute pressure (MAP) of anintake manifold to be maintained consistently in the third controlregion; controlling, by the controller, a throttle valve to be fullyopened, advancing an intake valve closing (IVC) timing, and controllingan exhaust valve closing (EVC) timing to after a top dead center in thefourth control region; and controlling, by the controller, a wide openthrottle valve (WOT) and retarding the intake valve closing in the fifthcontrol region.
 2. The method of claim 1, wherein, when the firstcontrol region is determined by the controller, the controller controlsthe intake valve closing (IVC) timing to be fixed and controls theexhaust valve closing (EVC) timing to be set up at a maximum valuewithin sustainable combust stability so as to limit a valve overlap. 3.The method of claim 1, wherein, when the second control region isdetermined by the controller, the controller controls the exhaust valveclosing (EVC) timing to be late as the engine load is increased suchthat the exhaust valve reaches the maximum duration.
 4. The method ofclaim 1, wherein, when the third control region is determined by thecontroller, the controller advances both the exhaust valve closing (EVC)timing and the intake valve closing (IVC) timing so as to maintain theMAP consistently when the engine load is increased.
 5. The method ofclaim 1, wherein, when the fourth region is determined by thecontroller, the controller retards the intake valve closing (IVC) timingand controls the exhaust valve closing (EVC) timing to approach a topdead center so as to inhibit from generating the valve overlap.
 6. Asystem for controlling valve timing of a continuous variable valveduration engine, the system comprising: a data detector configured todetect data related to a running state of a vehicle; a camshaft positionsensor configured to detect a position of a camshaft; an intakecontinuous variable valve duration (CVVD) device configured to controlan opening time of an intake valve of the engine; an exhaust continuousvariable valve duration (CVVD) device configured to control an openingtime of an exhaust valve of the engine; a controller configured toclassify a plurality of control regions depending on an engine speed andan engine load based on signals from the data detector and camshaftposition sensor and configured to control the intake CVVD device and theexhaust CVVD device according to the plurality of control regions,wherein the a plurality of control regions comprises: a first controlregion determined by the controller when the engine load is less than afirst predetermined load, a second control region determined by thecontroller when the engine load is greater than or equal to the firstpredetermined load and less than a second predetermined load, a thirdcontrol region determined by the controller when the engine load isgreater than or equal to the second predetermined load and less than athird predetermined load, a fourth control region determined by thecontroller when the engine load is greater than or equal to the secondpredetermined load and the engine speed is less than a predeterminedspeed, and a fifth control region determined by the controller when theengine load is greater than or equal to the third predetermined load andthe engine speed is greater than or equal to the predetermined speed;wherein the controller applies a maximum duration to the intake valveand limits a valve overlap by using the exhaust valve in the firstcontrol region, and the controller applies the maximum duration to theintake and exhaust valves in the second control region, controls amanifold absolute pressure (MAP) in an intake manifold to be maintainedconsistently in the third control region, controls a wide open throttlevalve (WOT) and advances an intake valve closing (IVC) timing andcontrols an exhaust valve closing (EVC) timing to after a top deadcenter (TDC) in the fourth control region, and controls a wide openthrottle valve (WOT) and retards the IVC timing in the fifth controlregion.
 7. The system of claim 6, wherein the controller controls theintake valve closing (IVC) timing to be fixed and controls the exhaustvalve closing (EVC) timing to be set up at a maximum value withinsustainable combust stability so as to limit a valve overlap in thefirst control region.
 8. The system of claim 6, wherein the controllercontrols the exhaust valve closing (EVC) timing to be late as the engineload is increased such that the exhaust valve reaches the maximumduration in the second control region.
 9. The system of claim 6, whereinthe controller advances both the exhaust valve closing (EVC) timing andthe intake valve closing (IVC) timing so as to maintain the MAPconsistently when the engine load is increased in the third controlregion.
 10. The system of claim 6, wherein the controller retards theintake valve closing (IVC) timing and controls the exhaust valve closing(EVC) timing to approach a top dead center so as to inhibit fromgenerating the valve overlap in the fifth control region.